1. Field of the Invention
The present invention generally relates to plasma processing apparatuses and, more particularly, to a plasma processing apparatus which processes a wafer for producing a semiconductor device by using a plasma generated by a microwave.
2. Description of the Related Art
Recently, in a semiconductor device manufacturing process, plasma processing apparatuses have been used to perform semiconductor producing processes such as a deposition process, an etching process or an ashing or stripping process since high-density integration and fine structure are required for semiconductor devices. Particularly, a microwave plasma processing apparatus has become popular since the microwave plasma processing apparatus is capable of generating stable plasma at a relatively low vacuum of 0.1 millitorr (mTorr) to several tens of mTorr. The microwave plasma processing apparatus generates high-density plasma by using a microwave or a combination of a microwave and a magnetic field generated by a ring-like coil. The above-mentioned plasma processing apparatus is disclosed in Japanese Laid-Open Patents No. 5-343334 and No. 9-181052.
A description will now be given, with reference to FIGS. 1 and 2, of a conventional microwave plasma processing apparatus. FIG. 1 is a schematic cross-sectional view of a conventional microwave plasma processing apparatus. FIG. 2 is a plan view of an antenna member provided in the microwave plasma processing apparatus.
In FIG. 1, the conventional microwave plasma processing apparatus 2 comprises: a process chamber 4; a table 6 provided inside the process chamber 4; an insulating plate 8 defining a top plate of the process chamber 4 and positioned above the table 6; and an antenna member 10 positioned above the insulating plate 8. The process chamber 4 is constructed so that air inside the process chamber 4 can be evacuated to generate a vacuum therein. The insulating plate 8 is formed of a material that can transmit a microwave.
The antenna member 10 has a flat, disk-like shape as shown in FIG. 2, and has a thickness of several millimeters. Above the antenna member 10 is a slow-wave member 16 formed of a dielectric material so as to reduce the wavelength of a microwave in radial directions of the antenna member 10. The antenna member 10 is provided with many slots 14 each of which has an elongated rectangular shape when viewed from a direction perpendicular to the flat surface of the antenna member 10. Generally, the slots 14 are arranged along concentric circles as shown in FIG. 2, or arranged along a spiral.
The plasma processing apparatus 2 has a coaxial waveguide 12 connected to a center portion of the antenna member 10 so as to introduce a microwave generated by a microwave generator (not shown in the figure) into the antenna member 10. The microwave introduced into the center portion of the antenna member 10 propagates through the antenna member 10 in radial directions thereof, and is directed downwardly toward the interior of the process chamber 4. The microwave introduced into the process chamber 4 generates plasma so that a wafer W placed on the table 6 in the process chamber 4 is subjected to predetermined plasma processing such as plasma etching or deposition.
FIG. 3 is an enlarged plan view of the slot 14 formed in the antenna member 10. FIG. 4 is a cross-sectional view of a part of the antenna member 10 taken along a line IVxe2x80x94IV of FIG. 2.
As shown in FIG. 3, each of the slots 14 has a rectangular shape having a width L1 of between 10 and 20 millimeters and a length L2 of about several tens of millimeters. The inner walls 14A of the slot 14 are perpendicular to the flat surface of the antenna member 10.
It is known that a microwave causes concentration of an electric field near a sharp corner when the microwave propagates in a solid medium. Thus, when the microwave propagates within the antenna member 10 in radial directions from the center portion thereof, a concentration of the electric field occurs at each corner 14B of the slot 14 and each edge between the inner wall 14A and a flat surface of the antenna member 10. When such a concentration of an electric field occurs, the plasma density is locally increased, and, thereby, an abnormal discharge occurs at the position where the electric field density is increased. This results in unevenness of the plasma density over the entire surface of the wafer.
Additionally, in a case in which a rectangular opening is positioned perpendicular to a radial direction of the antenna member 10, an abnormal discharge frequently occurs between the opposite longer sides of the rectangular opening at a middle position between the shorter sides when the power of the microwave is large.
In order to avoid such a problem, the plasma processing must be performed with an input power level at which the above-mentioned problem does not occur. In this case, there is a problem in that the throughput of the semiconductor manufacturing process is greatly decreased since the ability to increase the plasma density is limited.
Additionally, the above-mentioned Japanese Laid-Open Patent Application No. 5-343334 discloses a slot formed by two copper-plate antennas stacked on each other so that the area of opening of the slot can be changed by rotating the copper-plate antennas relative to each other. In such a case, since a single slot is formed by the two copper-plate antennas in the stacked state, a step is formed in the stacked portion of the slot. Thus, there may be a problem in that an abnormal discharge is generated due to the concentration of electric field at the stacked portion.
It is a general object of the present invention to provide an improved and useful flat antenna of a plasma processing apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a flat antenna of a plasma processing apparatus to which a high power level can be supplied without generation of an abnormal discharge.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a flat antenna adapted to be used for introducing a microwave into a process chamber so as to generate a plasma within the process chamber, the flat antenna comprising: a front surface to which the microwave is supplied and a back surface opposite to the front surface, the microwave being supplied to a center portion of the front surface and propagating in radial directions within the flat antenna; and a plurality of openings extending between the front surface and the back surface of the flat antenna, a contour of each of the openings being curved so as to prevent generation of an abnormal discharge.
According to the present invention, there is no sharp angle corner formed by each of the openings. Thereby, an electric field generated by the microwave transmitting through the flat antenna is not concentrated due to a sharp angle corner. Thus, the possibility of generation of an abnormal discharge at or in the vicinity of openings is reduced.
In one embodiment of the present invention, each of the openings may have an elongated elliptic shape. Alternatively, each of the openings may have a polygonal shape with rounded corners.
Additionally, the openings may be arranged along a plurality of concentric circles or a spiral so that the openings are evenly distributed over the entire flat antenna.
Additionally, there is provided according to another aspect of the present invention a flat antenna adapted to be used for introducing a microwave into a process chamber so as to generate a plasma within the process chamber, the flat antenna comprising: a front surface to which the microwave is supplied and a back surface opposite to the front surface, the microwave being supplied to a center portion of the front surface and propagating in radial directions within the flat antenna; and a plurality of pairs of openings having an elongated elliptic shape, each of the openings extending between the front surface and the back surface of the flat antenna, each pair consisting of a first opening and a second opening positioned perpendicular to the first opening so that each two adjacent openings form a T-like shape.
According to this invention, a circularly polarized microwave is generated and radiated from the flat antenna. That is, a current flowing from the center of the flat antenna first reaches the first opening, and then reaches the second opening in the same pair. Thus, the circularly polarized microwave is radiated from the pair of the first and second openings. Since the circularly polarized microwave does not generate a concentrated electric field near an edge of a wafer placed inside a process chamber of the plasma processing apparatus, a uniform plasma can be applied over the entire wafer.
The flat antenna according to the present invention is applied to a plasma processing apparatus so that uniform plasma is generated in the plasma processing apparatus.
Other objects, features and advantages of the present invention will become more apparent from the detailed description when read in conjunction with the accompanying drawings.